The present invention relates to a wireless device and a wireless channel measurement controller, and more particularly to a technology related to a channel selection method for wireless channel measurement in the IEEE 802.11 wireless local area network (WLAN).
A wireless local area network (WLAN) is basically composed of a base station (access point; AP) and called stations (stations; STAs) (both the base station and the stations are also called wireless terminals). The stations and the access point that are within the same radio coverage are known as a basic service set (BSS). When such BSSs are located close to each other and operate at the same channel, which are referred to as overlapping BSSs, it is difficult to support required quality-of-service due to possible contentions between the overlapping BSSs. To avoid such problems, if channel interference occurs persistently in one or more stations and/or the access point in a particular BSS, the access point dynamically selects a new wireless link to maintain the operation of the BSS.
To dynamically select a channel for communication between a plurality of stations and the access point located within the coverage of a BSS, among available wireless channels, the access point first determines whether or not the channel being used in the current communication by a plurality of wireless terminals is an appropriate channel, that is, whether or not selection of a new channel better in communication state is needed, and then requests a subset of stations to make a channel signal quality measure. To achieve this process, a set of channels available to the stations is determined. Using the determined set of available channels, detected are whether or not a signal of a channel identical to one included in the set of available channels has been received from an adjacent BSS, and whether or not there is radio interference from an adjacent BSS in any of the set of available channels. The stations measure the communication states of these available channels, and report the packet error rate (PER) and the received signal strength indication (RSSI) of all the channels measured by the stations to the access point. The interference level is also measured, which is the level of interference occurring due to an effect of any other wireless device during a given time. The interference level is based on the absence of signal reception from another BSS while a station in this BSS measures a signal and reports the measurement result to the access point. Thereafter, a new channel conforming to the decision criteria of the access point is selected based on the measure of the received signal strength indication, the packet error rate and the interference level information.
FIG. 2 shows part of the configuration of a conventional wireless communication system (wireless device). A wireless communication system 20 of FIG. 2 includes: a transmit/receive part 23 having a channel measurement section 22 for performing channel measurement; and a host part 21 for receiving measurement results from the channel measurement section 22. Conventionally, measurement of wireless channels is made by a wireless communication system having such a channel measurement section 22.
As a related technology, US 2002/0060995A describes a method for measuring channels to determine a new channel.
Also, IEEE 802.11h examines a technique of measuring the states of wireless channels to dynamically change a channel.
However, although measurement of wireless channels has been discussed in the literature on the channel measurement technology described above, no mention has been made of a specific measurement method (algorithm).
FIG. 13 is a view showing channels available in Japan as of December 2004, while FIG. 14 is a view showing channels available in the U.S. While the number of channels available in Japan is four (5150 to 5250 [MHz]) as shown in FIG. 13, multiple channels (eight channels; 5150 to 5350 [MHz]) are available in North America as shown in FIG. 14. (Note that from May 2005 the eight channels available in North America are also available in Japan.) When the number of available wireless channels is large, the interval required until the same channel is measured next will be long if all of these wireless channels are measured in rotation, causing the problem of increasing the entire measurement time.